It has been known that in order to ensure that plastic auto parts have a coat of paint thereon which adheres well, the parts must be degreased before they are painted in order to remove the mold releasing agent, which has been used to ensure the release of the plastic parts from the plastic mold. The necessity for degreasing articles to be painted is, of course, not limited to automobile parts, but extends to any part which has an oily coating, which must be removed before the article can be properly painted.
The conventional method of degreasing such parts is to pass them through a vapor bath formed from a degreasing solution, for example 1.1.1 trichloroethane. A reservoir of degreasing solution is provided in the degreasing apparatus, and a heater is provided in the reservoir, which, upon being heated, vaporizes the degreasing solution to form a vapor both of the degreasing solution in a vapor space immediately above the reservoir.
In the art of degreasing plastic automobile parts, particularly bumpers and the like, the degreasing apparatus has been provided with a cooling coil which extends around the upper part of the apparatus to limit the height to which the vapor can escape. The cooling coil effectively condenses the vapor which attempts to rise higher than the cooling coil, and the condensed vapor is normally returned to the reservoir of degreasing solution. One such apparatus is disclosed in Published Japanese Application No. 61-178083, published Aug. 9, 1961. In this published application, FIG. 4 shows the conventional apparatus, in which the cooling coil 4 limits the vapor space to the position of the chain line in the tank 1 of the degreasing apparatus.
In an apparatus for painting automobile parts by conveying them past a painting station where plastic parts, such as automobiles bumpers, are being painted, it is sometimes necessary to increase or reduce the speed of the painting conveyor depending upon the conditions at the point where the parts are being painted. In a continuous production process, the parts, such as bumpers, coming from the molding operation, are fed through a degreasing apparatus on a degreasing conveyor, and then transferred through a discharge-feed station and fed to the painting conveyor. The degreasing conveyor is conventionally run at a speed which attempts to match the speed of the painting conveyor as closely as possible. However, when the painting conveyor is slowed down too much, the degreasing conveyor reaches a lower limit, and at a speed below this lower limit, the plastic parts, such as bumpers, remain in the vapor both formed from the degreasing solution for a period which is too long, and the vapor tends to penetrate the plastic, which results in an imperfect adherence of the paint to the plastic part.
Heretofore, as shown in FIG. 1, in order to accommodate the mismatch of the speed of the degreasing conveyor A, where the painting conveyor B has been slowed down below the speed at which a corresponding speed of the degreasing conveyor A will hold the parts in the degreasing apparatus for too long a period of time, a buffer transfer apparatus is used to transfer the degreased bumpers from the degreasing conveyor A to the painting conveyor B. The buffer transfer apparatus can, when the speeds of the respective conveyors are more or less matched, transfer the parts directly from the degreasing conveyor to the painting conveyor. However, when the painting conveyor slows down too much, it diverts some of the parts to storage, and, when the painting conveyor then resumes a speed which is greater than that of the degreasing conveyor, the stored parts are brought back through the buffer transfer apparatus for transfer to the painting conveyor B.
As can be understood, the use of a buffer transfer apparatus increases the complexity and expense of the apparatus, requires a larger floor space, particularly for the storage facility, and can create difficulties in the operation of the degreasing and painting process if the buffer transfer apparatus fails to operate properly.